Dehydroaromatization of methane over Mo/ZSM-5 zeolites: influence of aluminum distribution in the crystals
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Dehydroaromatization of methane over Mo/ZSM‑5 zeolites: influence of aluminum distribution in the crystals Michal Horňáček1 · Pavol Hudec1 · Vladimír Jorík1 · Mária Čaplovičová2 · Ľubomír Čaplovič3 · Michal Kaliňák1 · Agáta Smiešková1 Received: 25 February 2020 / Accepted: 8 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Mo/ZSM-5 type catalysts based on two ZSM-5 zeolites with comparable crystal morphology, shape and size, Si/Al in bulk (22–23), acidity and amount of Mo (~ 4.7 wt.%) but having a different (homogeneous and non-homogeneous) Al distribution in particles and different acid sites type distribution were investigated in methane dehydroaromatization. From the results follows that Mo is associated with both BAS and LAS in the samples with almost homogenous Al distribution (MoZSM-5/AH). In the case of both samples with non-homogenous Al distribution (MoZSM-5/BH and MoZSM-5/BNH4) Mo preferably associates with BAS. Evidently lower activity and selectivity of Mo/ZSM-5/AH catalyst in methane transformation compared with Mo/ZSM-5/BH we attribute to the fact that from Mo species which interact with Lewis acid sites in sample ZSM-5/AH less active carburized species are formed as from the Mo associated with Brønsted sites in sample ZSM-5/BH. Keywords Aromatization · Methane · Mo/zsm-5 · Al distribution in zeolite particles
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1114 4-020-01887-5) contains supplementary material, which is available to authorized users. * Michal Horňáček [email protected] 1
Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovak Republic
2
University Science Park Bratislava Centre, Slovak University of Technology in Bratislava, Vazovova 5, 812 43 Bratislava, Slovak Republic
3
Faculty of Materials Science and Technology, Slovak University of Technology in Bratislava, Paulínska 16, 917 24 Trnava, Slovak Republic
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Reaction Kinetics, Mechanisms and Catalysis
Introduction Since the first report published in 1993 [1] that MoZSM-5 catalyst was active in the transformation of methane into aromatics in non-oxidative conditions an intensive research proceeds centered on the investigation of the efficient catalyst. The methane conversion into more valuable chemicals is much more difficult to perform than the other saturated hydrocarbons because methane is the least reactive among alkanes. Because of a great significance of zeolite supported catalysts in this reaction number of works have been devoted to the study of this type of catalyst. The important advances in the above-mentioned field of research are summarized in [2]. In many works was concluded that the most effective catalysts for this process is MoZSM-5 e.g. [1, 3–5]. Dehydroaromatization (DHA) of methane is equilibrium limited reaction. In work of Z.R. Ismagilov and co-workers [6] is presented the theoretically possible yield of aromatic hydrocarbons (benzene
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